This invention relates to the use of dried cells which can be stored, rehydrated and used as controls or standards, and in particular, relates to the use of mammalian cells fixed with a fixative, reduced with a Schiff's base reducing agent and then freeze-dried in the presence of trehalose which when rehydrated retain their light scatter properties and labelling properties when labelled with cell markers such that they can be used as standards or controls in cellular analysis such as flow cytometry and other forms of image analysis.